1. Field of the Invention
The present invention generally relates to a stapler for stapling sheets of paper, sheets of corrugated cardboard, sheets of thin plywood, or the like, and particularly relates to a stapler in which a slip or the like can be stapled on such sheets of paper, sheets of corrugated cardboard, or the like, without putting any base member acting as a staple matrix against the rear surface of the sheets.
2. Description of the Prior Art
A stapler is widely used, for example, in the case where a plurality of forms are bundled up into a form of accumulation or in the case where flaps of a paper box or a corrugated carton are fastened. Taking into consideration capability of penetrating meterials to be stapled, each of staples used for such a stapler as described above is formed of a linear body of wire and provided with a supporting portion and a pair of parallel stapling leg portions extending from the opposite ends of the supporting portion substantially perpendicularly thereto. The stapler is constituted by three members, that is, a base member having a matrix in which a bending groove for bending the stapling leg portions of a staple is formed; a staple supporting member accommodating staples and having a staple drive-out opening formed in opposition to the bending groove; and a pressing lever member disposed behind the staple drive-out opening for pressing the staples toward the staple drive-out opening. These three members are pivotally supported at an end portion of the staple supporting member opposite to the stable drive-out opening. Further, the staples are pressed by the pressing lever member toward the staple drive-out opening in the staple supporting member so that forward one of the staples is always located at the staple drive-out opening.
In stapling, a stack of sheets of paper to be stapled are inserted between the matrix of the base member and the staple supporting member so as to bring a portion to be stapled of the stack of sheets into the position where the matrix and the staple drive-out opening are faced to each other, and the pressing lever member is pressed down toward the base member. Then, the forwardmost one of the staples is pinned ino the stack of sheets through the staple drive-out opening to pass through the stack of sheets. Both the forward free ends of the stapling leg portions of the staple abut on the groove bottom of the bending groove in the matrix and then bent by about 90 degrees along the shape of the groove bottom of the bending groove by the pressure exerted by the pressing lever member, so that the sheets of paper are stapled between the matrix of the base member and the staple supporting member into a stapled accumulation.
In such a stapler as described above, however, it is necessary to insert sheet materials between the matrix of the base member and the staple supporting member in order to bend both the forward ends of stapling leg portions of a staple. Therefore, stapling cannot be carried out in the case where the distance between an edge of the sheet materials and a portion to be stapled of the same sheet materials is longer than the distance between the drive-out opening of the stapler and the pivotal point of the three members, that is, the base member, the staple supporting member, and the pressing member. Particularly, in the case where flaps of corrugated carton of various sizes are stapled, there has been such a disadvantage that it is necessary to prepare a stapler which is so designed that the distance between the drive-out opening of the stapler and the pivotal point of the above-mentioned three members is selected to be substantially equal to the maximum distance between an edge of flaps and a portion to be stapled of corrugated carton of various sizes.
Accordingly, the inventor of this application has proposed a stapler by which sheets of paper or the like can be stapled without using any base member, as disclosed in Japanese Utility Model Unexamined Publication No. 61-89482 laid open June 11, 1986 (Japanese Utility Model Registration Application No. 59-174937 filed Nov. 20, 1984). In this stapler, staples each having a pair of stapling leg portions which have been curved inward at an extent in advance are used, and a push-out guide is provided so that when one of the staples is pushed out through a staple drive-out opening of a staple supporting member, the stapling leg portions of the staple are forced to further bend inward. As a result, the stapler can be bent without being guided by a matrix of a base member, and therefore stapling can be easily carried out by only putting the stapler on a desired portion of the upper surface of materials to be stapled and pushing out one staple by a pressing lever member of the staple. This stapler is effectively used particularly in the case where an address tag or the like is temporarily attached on a corrugated carton. In the foregoing stapler, however, there has been a disadvantage in that the stapler is so complicated in structure that mass production cannot be carried out on the stapler and therefore the stapler cannot be provided at a low cost.